This section provides background information related to the present disclosure which is not necessarily prior art.
Articles of footwear conventionally include an upper and a sole structure. The upper may be formed from any suitable material(s) to receive, secure, and support a foot on the sole structure. The upper may cooperate with laces, straps, or other fasteners to adjust the fit of the upper around the foot. A bottom portion of the upper, proximate to a bottom surface of the foot, attaches to the sole structure.
Sole structures generally include a layered arrangement extending between a ground surface and the upper. One layer of the sole structure includes an outsole that provides abrasion-resistance and traction with the ground surface. The outsole may be formed from rubber or other materials that impart durability and wear-resistance, as well as enhance traction with the ground surface. Another layer of the sole structure includes a midsole disposed between the outsole and the upper. The midsole provides cushioning for the foot and may be partially formed from a polymer foam material that compresses resiliently under an applied load to cushion the foot by attenuating ground-reaction forces. The midsole may additionally or alternatively incorporate a fluid-filled chamber to increase durability of the sole structure, as well as to provide cushioning to the foot by compressing resiliently under an applied load to attenuate ground-reaction forces. Sole structures may also include a comfort-enhancing insole or a sockliner located within a void proximate to the bottom portion of the upper and a stroble attached to the upper and disposed between the midsole and the insole or sockliner.
Midsoles using fluid-filled chambers are generally configured as a chamber formed from two barrier layers of polymer material that are sealed or bonded together, and pressurized with a fluid such as air, and may incorporate tensile members within the chamber to retain the shape of the chamber when the chamber compresses resiliently under applied loads, such as during athletic movements. Generally, fluid-filled chambers are designed with an emphasis on balancing support for the foot and cushioning characteristics that relate to responsiveness as the fluid-filled chamber resiliently compresses under an applied load. The fluid-filled chamber as a whole, however, fails to adequately provide support for the foot, as well as an acceptable level of traction between the outsole and the ground surface, during directional shifts between successive ground-reaction forces during athletic movements, thereby resulting in the foot being unstable in preparation for a next athletic movement. Accordingly, creating a midsole from a fluid-filled chamber that provides acceptable traction between the outsole and the ground surface and adequate support for the foot while attenuating ground-reaction forces applied in different directions is difficult to achieve.
Corresponding reference numerals indicate corresponding parts throughout the drawings.